A signal corresponding to a high-frequency band is less sensitive to a fine structure of frequencies in comparison to a signal corresponding to a low-frequency band. Accordingly, in order to increase coding efficiency to cope with restrictions of allowable bits when an audio signal is encoded, a signal corresponding to a low-frequency band is encoded by allocating a relatively large number of bits and a signal corresponding to a high-frequency band is encoded by allocating a relatively small number of bits.
The above-described method is used in spectral band replication (SBR). In SBR, a lower band of a spectrum, e.g., a low-frequency band or a core band, is encoded and an upper band, e.g., a high-frequency band, is encoded by using parameters, e.g., an envelope. SBR uses correlations between lower and upper bands such that characteristics of the lower band are extracted to predict the upper band.
In SBR, an improved method for generating a bandwidth extended signal for a high-frequency band is required.